U.S. Pat. No. 3,817,659 assigned to Kobe, Inc., assignee of this application, describes a pitot pump having many features in common with this development. Broadly, such a pitot pump has a fixed housing within which is mounted a rotatable casing. A fixed pitot tube is mounted in the casing for withdrawing fluid from near the periphery of the casing as it rotates. This results in high pressure fluid that is discharged through an axial passage through an end wall of the rotatable casing. Fluid is introduced to the interior of the casing through an annular passage surrounding the pitot pump outlet and then through a plurality of radiating passages in the end wall of the casing. Such pumps operate for long periods at high efficiency.
A pitot pump of this type may operate with approximately ambient pressure at the fluid inlet. When this is the case there is no significant axial thrust by the casing on the bearings on which it is mounted. The pitot pump described in U.S. Pat. No. 3,817,659 includes a jet pump connected to the pump inlet to increase the net positive suction head for enhancing the pitot pump discharge. Other means may also be employed for pressurizing the pitot pump, such as, for example, operation in an essentially closed system wherein the inlet pressure may be a few hundred psi. During such operation, there is a net thrust load on the casing corresponding to the pressure of the inlet fluid and the area of the inlet passage. Except for this area, pressure forces induced by the fluid balance out to have no net thrust.
U.S. Pat. No. 3,822,102 provides a means for balancing the thrust load in a multi-stage pitot pump. This is done by providing an axial chamber at the opposite end of the rotatable casing from the fluid inlet. The interior of this balancing chamber is in fluid communication, by way of a tube, with the inlet passage to the pump. This essentially balances the areas on which pressure acts, thereby minimizing axial thrust.
Such an arrangement is suitable for a multi-stage pitot pump where the pressure to be balanced is present due to pressure differential between the stages. It is not appropriate for a single-stage pitot pump having a pressurized fluid inlet. It is therefore desirable to provide means for minimizing the thrust load on the bearings supporting the rotatable casing of a pitot pump for use with pressurized inlet fluid.